1. Field of the Invention
The present invention relates to a wavelength tunable laser light source necessary for a Wavelength Division Multiplexing (WDM)-based optical communication system, and more particularly, to a wavelength tunable laser for maintaining a stable wavelength without a wavelength locker.
2. Description of the Related Art
As the amounts of information transmitted over the communication system explosively grow, Wavelength Division Multiplexing (WDM)-based optical communication becomes prevalent for high speeds networks. WDM is a technology that utilizes optical signals having different wavelengths (channels) to be transmitted through a single optical fiber, taking advantage of the non-interactivity of light. Recognized as a powerful and cost-effective optical communication solution, the WDM technology guarantees the scalability and the flexibility of the optical communication system.
In a WDM-based optical communication system, a wavelength tunable laser becomes more important than ever before as a multi-channel light source or a back-up light source. For such applications, the wavelength tunable laser light source should show a good single mode operation (a side mode suppression ratio should be 30 dB or higher), wavelength stability (xc2x15% or less of channel separation), and high output power. In addition, a low cost wavelength tunable laser will be a key device in metro and subscriber networks that are expected to evolve at a rapid pace.
However, an existing wavelength tunable laser has a problem to obtain stable lasing wavelength because it is sensitive to change in current, temperature, and environments. As a solution to the above problem, a wavelength locker is used to monitor the lasing wavelength and adjust the wavelength actively using the monitored value. The wavelength locker has several disadvantages such as high cost, complex packaging process, and need of complex wavelength control circuit. Further, periodical calibrations should be performed to calibrate the change in device module caused by aging of the semiconductor laser diode and of the wavelength control circuit. That is, the expensive wavelength tunable laser including the wavelength locker and a complicated control circuit is not suitable for metro and the subscriber networks in which cost is the main concern.
To solve the above-described problems, it is an object of the present invention to provide a wavelength tunable laser that is cost-effective and can maintain excellent wavelength stability without a wavelength locker.
To achieve the above object, a wavelength tunable laser light source according to a 1st embodiment of the present invention includes:
an optical fiber that implements multiple reflection peaks; and
a semiconductor device that contains one facet adjacent to the optical fiber, which has an antireflection coating, and a mode size converter section, a gain section and a distributed Bragg reflector (DBR) mirror section.
By the antireflection coating, the optical fiber and the semiconductor device are optically coupled. So, laser oscillation wavelength is determined by coupled reflection spectra of both the optical fiber and DBR mirror.
In the above embodiment, the semiconductor device can further include a phase control section. The optical fiber contains multiple fiber Bragg gratings or a sampled fiber Bragg grating in order to implement multiple reflection peaks. The DBR mirror section contains a single Bragg grating or a sampled Bragg grating and the reflection peak(s) can be controlled by current injection.
A wavelength tunable laser according to a 2nd embodiment includes:
an optical fiber that implements multiple reflection peaks; and
a semiconductor device that contains one facet adjacent to the optical fiber, which has an antireflection coating, and a mode size converter section, a gain section and a tunable wavelength filter section.
By the antireflection coating, the optical fiber and the semiconductor device are optically coupled. So, laser oscillation wavelength is determined both by reflection peaks of the optical fiber and filtering curve of tunable wavelength filter section.
In the above embodiment, the semiconductor device can further include a phase control section. The optical fiber contains multiple fiber Bragg gratings or a sampled fiber Bragg gratings in order to implement multiple reflection peaks. The variable wavelength filter section has a coupled optical waveguide for filter operation.
A wavelength tunable laser light source according to a 3rd embodiment of the present invention includes:
an optical fiber that implements multiple reflection peaks;
a semiconductor device that contains one facet adjacent to the optical fiber, which has an antireflection coating, and a gain section and a DBR mirror section; and
a lens for being positioned between the optical fiber and the semiconductor device.
By the antireflection coating, the optical fiber and the semiconductor device are optically coupled. The coupling efficiency between them is improved by the incorporation of the lens. So, laser oscillation wavelength is determined by coupled reflection spectra of both the optical fiber and DBR mirror.
In the above embodiment, the semiconductor device can further include a phase control section. The optical fiber contains multiple fiber Bragg gratings or a sampled fiber Bragg grating in order to implement multiple reflection peaks. The DBR mirror section contains a single Bragg grating or a sampled Bragg grating and the reflection peak(s) can be controlled by current injection.
A wavelength tunable laser light source according to a 4th embodiment of the present invention includes:
a silica Passive Lightwave Circuit (PLC) that implements multiple reflection peaks by multiple Bragg gratings or a sampled Bragg grating in a waveguide realized on PLC; and
a semiconductor device that is flip-chip bonded on the PLC substrate, that contains one facet adjacent to the waveguide of the silica PLC, and the facet has an antireflection coating, and a mode size converter section, a gain section and a DBR mirror section.
By the antireflection coating, the PLC waveguide and the semiconductor device are optically coupled. So, laser oscillation wavelength is determined by coupled reflection spectra of both the PLC waveguide and DBR mirror.
In the above embodiment, the semiconductor device can further include a phase control section. The optical fiber contains multiple fiber Bragg gratings or a sampled fiber Bragg grating in order to implement multiple reflection peaks. The DBR mirror section contains a single Bragg grating or a sampled Bragg grating and the reflection peak(s) can be controlled by current injection.
With the embodiments described above, a cost-effective and highly wavelength stable wavelength tunable laser could be realized without a wavelength locker and a complex controlling circuit.